1. Field of the Invention
The present invention relates to a semiconductor device having a fine wire.
2. Description of Related Art
In a semiconductor device, a wire made of a metallic material such as Al (aluminum) or Cu (copper) is formed on a semiconductor substrate provided with elements such as transistors through an interlayer dielectric film.
When a metallic material mainly composed of Al is employed as the material for the wire, for example, the wire (Al wire) is formed on a planar surface of the interlayer dielectric film.
When a metallic material mainly composed of Cu is employed as the material for the wire, on the other hand, the wire (Cu wire) is embedded in a trench formed in the interlayer dielectric film. The Cu wire is superior to the Al wire in a point that the same has smaller wiring resistance.
Semiconductor devices having multilayer interconnection structures include that employing Cu wires. In this semiconductor device, a first trench is formed in a first interlayer dielectric film formed on a semiconductor substrate, and a lower wire made of Cu is embedded in this first trench. A second interlayer dielectric film is laminated on the first interlayer dielectric film having the Cu wire embedded therein. A second trench is formed in the second interlayer dielectric film. Further, a via hole reaching the upper surface of the lower wire from the bottom surface of the second trench is formed in the second interlayer dielectric film. An upper wire as Cu wire is embedded in the second trench, while a via made of a metallic material mainly composed of Cu is embedded in the via hole. Thus, the upper and lower wires are electrically connected with each other through the via.
The uppermost Al or Cu wire is covered with a passivation film. In the multilayer interconnection structure, the Al or Cu wire other than the uppermost wire is covered with the interlayer dielectric film.
The interlayer dielectric film or the passivation film covering the corresponding wire (Al or Cu wire) is formed by CVD (Chemical Vapor Deposition), for example, after formation of the wire. The interlayer dielectric film or the passivation film is formed by CVD in a CVD apparatus under a high temperature of 300 to 400° C. After the formation of the interlayer dielectric film or the passivation film, therefore, the semiconductor device is taken out from the CVD apparatus, to be abruptly cooled to room temperature. At this time, the coefficients of thermal contraction of the metallic material forming the wire and an insulating material forming the interlayer dielectric film or the passivation film are so different that the interlayer dielectric film or the passivation film hinders contraction of the wire. Consequently, remarkable stress resulting from the thermal contraction difference between the wire and the interlayer dielectric film or the passivation film is applied to the wire.
In the conventional semiconductor device, the width of the wire is so large that the wire is not disconnected even if stress resulting from the thermal contraction difference between the wire and the interlayer dielectric film or the passivation film is applied thereto. In the semiconductor device including the Al wire, the Al wire is formed by stacking a layer made of Al and a layer made of a high-melting metal such as Ti (titanium), TiN (titanium nitride), TiW (titanium tungsten), Ta (tantalum) or TaN (tantalum nitride), and hence the wire is not disconnected even if stress resulting from the thermal contraction difference between the wire and the interlayer dielectric film or the passivation film is applied to the wire.
However, it has been recognized that, if the width of the wire is reduced to not more than 0.4 μm in order to refine the wire, the wire is disconnected when stress resulting from the thermal contraction difference between the wire and the interlayer dielectric film or the passivation film is applied thereto.